A thermopile can include an electronic device that converts thermal energy into electrical energy. It can be composed of several thermocouples often connected in series or in parallel. Thermopiles do not respond to absolute temperature, but generate an output voltage proportional to a local temperature difference or a temperature gradient. The output voltage of a thermopile can be in the range of tens or hundreds of microvolts. A thermopile can be used to generate electrical energy from, for instance, heat from electrical components, solar wind, radioactive materials, or combustion.